A billet is the place to which a person, generally a soldier, is assigned to sleep. Soldiers are generally billetted in barracks when on duty, although in some armies soldiers with families are permitted to maintain a home off-post.

One of the major grievances of the American colonists against the British government which led to the American Revolutionary War was the quartering of soldiers in civilian homes. As a result, the Third Amendment to the United States Constitution provides restrictions on the manner in which the Federal government may require civilians to provide housing for American soldiers.

During wartime, civilians who have been evacuated from a city in danger of attack are billetted in communual shelters or in the homes of individuals. The practice of billetting evacuees was widespread in Britain during World War II, particularly during the Blitz, when children and other non-essential persons in London were sent north to protect them.

More broadly, members of the armed forces often use the term "billet" to refer to their assignment or duty station, as well as their literal bunk or bed.

In metallurgy, a billet is a semi-finished length of metal to be worked in a rolling mill or other process. It may also be known as a bloom, slab or sheet-bar .